As the electronic devices integrate more functions and own higher performance, the structure and technology become more complicated. As in smart battery management system, the interface circuit conventionally has two control methods. One method is applying traditional analogy circuit for control. However, the traditional analogy circuit could not be complicated enough to meet the requirement of smart battery management, and also has high cost. The other method is applying digital coding to achieve fully digital control. Generally, a digital interface circuit is simple and easy to expand. With the advantages of quick response, high integration and easy control, the digital interface circuit represents the developing trend in the area of smart power management.
In the digitally controlled smart battery management system, it conventionally utilizes system management bus (SMBus) for control. The digital interface circuit is in the front-side thereof, configured to receive and to transfer relevant information signals from system management bus. When the digital coding is applied, the digital interface circuit may comprise a plurality of registers, e.g. control registers, buffer registers, data registers, and etc. The control registers comprise status-machines which control and coordinate with other registers for completing the transfer procedure, for example, to confirm the bit number of smart charging states, or to confirm the data bit number of each status.
FIG. 1 illustrates a schematic diagram of a prior art control register. As shown in FIG. 1, a digital interface 110 is in the front side of a control circuit 100 and comprises registers 111 and 112, wherein register 111 is a transmission state register comprising a first state machine configured to confirm the transmission status of the SM bus. Register 112 is a state counter register comprising a second state machine configured to confirm the corresponding data bit number of transmission of a corresponding control instruction under each transmission status, and to synchronize it with external serial clock line (SCL) of the smart battery system. The transmission state register 111 and the state counter register 112 together comprise the control register, configured to generate control signals to an instruction bus 113 in control circuit 100. However, excessive numbers of registers may be adverse for integration and increase the cost.